How many stretches add up to the figure
An investigator looks through a list of movements for every unbroken stretch that comes to a particular amount.
- Only consecutive movements count as a stretch.
- Stretches may overlap, and every one of them counts separately.
- Movements can be negative, so a longer stretch is not always a bigger total.
- Return how many stretches come to exactly the target.
stretchesTotalling(movements: list<int>, target: int) → int
Go needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
func stretchesTotalling(movements []int, target int) int {
}Worked examples
| Call | Result |
|---|---|
stretchesTotalling([]int{1, 1, 1}, 2) | 2 |
stretchesTotalling([]int{1, 2, 3}, 3) | 2 |
stretchesTotalling([]int{1, -1, 0}, 0) | 3 |
stretchesTotalling([]int{}, 0) | 0 |
Hint
If the running total at two points differs by the target, the stretch between them is a hit. Keep a count of every running total you have seen and look up total minus target.
Reference solution in Go
func stretchesTotalling(movements []int, target int) int {
seen := map[int]int{0: 1}
running, hits := 0, 0
for _, movement := range movements {
running += movement
hits += seen[running-target]
seen[running]++
}
return hits
}